Cyclic carbamates and method for their



CYCLIC CARBAMATES AND METHOD FOR-THEIR PREPARATION Erhart K. Drechsel, Springdale, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application August 9, 1952, I Serial No. 303,609

3 Claims. (Cl. 260-444) This invention relates to the production of cyclic carbam'at'es or urethanes representedl' by' the general formula-- where n represents a: whole number selectedfrom the class consisting of 3 and 4. The cyclic carbamatesembraced by this formula are 2-ketotetrahydro-1,3-oxazine, which also may be named O,N-trimethylenecarbamate, and Z-ketohexahydro-1,3-oxazepine, which also may be named O,N-tetramethylenecarbamate. They have many valuable uses in industry, for example as plasticizers 'of resinous and other materials, and as intermediates in the production of other valuable compositions. They constitute a particularly useful class of monomers from which polymeric products are produced by isomerization. The solid, higher-molecular-weight polymers: (e; g.', those having an average molecularweight not less than 10,000, more particularly an average molecular weight: ranging from 10,000 or 20,000 to 75,00001' 100,000 or higher, as determined from viscosity measurements of dilute solutions using the Staudinger. equation are: fiber-forming polymers from which fibersor filaments having particular and peculiar properties can be'produced. Fibers or filaments: comprising or composed of polymerization productsor" the carbamatesr embraced by Formula I are included: within the scope of this invention,.:more. particularly those drawn or stretched fibers formed of polymers of the cyclic carbamate that have an average molecular weight of not less than 10,000", which fibers? show, by characteristic X-ray patterns, orientation along the fiber axis. The solid polymers of: the cyclic' carbama'tes embraced by Formula I are useful in coating, molding, laminating, adhesive, textile-treating, paper-treating and other applications where other synthetic resinsare now being used.

Various methods can be employed for producing the cyclic carbamates. embraced by Formula I. One convenient and economical method comprises efiecting' a Beckmann rearrangement of the corresponding hydroximic acid represented by the general formula Where n has the same meaning as given above with reference to Formula I, and then isolating a cyclic carbamate corresponding to the hydroximie acid employed from. the resulting reaction mass, e. g., by distillation under, heat and vacuum.

The: Beckmann rearrangement .as-applied to'other: compounds is well known in chemistry" (see, for instance,

Patented May 8, 1956 2. Sidgwicks The Organic Chemistry of Nitrogen, new edition, revised and rewritten by Taylor and. Baker, 1937, especially pages 1 9', 49, 177, 199-201, 472 and 57 3; also, U. S. Patents 2,249;177 and 2,234,566). The equation for this reaction (Beclcmann rearrangement) may be written as follows:

The hydroximic acids embraced by Formula II can be produced by various methods; for example, they may be prepared by the reactions represented by the following equations:

In Equations III and IV, n has the same meaning as given above withreference to Formulas I and II.

Another suitable methodfor preparing one of the cyclic carbamates embraced by Formula I, specifically 2-ketotetrahyclro-1,3-oxazine, comprises eifecting alcoholysis of N-(S-hydroxypropyl)-O-alkyl carbamate under heat, and isolating, Z-ketote'trahydro-l,3-oxazine from the resulting reactionmass. (This method is claimed in my copending, divisional application Serial No. 372,405, filed August 4, 1953-, now Patent'No; 2,701,246 dated February 1, 1955.) The O-al'kyl substituent is preferably an O-(lower alkyl) substituent, e. g;, O-methyl, -ethyl, -propyl, -isopropyl, -n-butyl', -isobutyl, -sec.-butyl, amyl, etc. Thus, I may prepare Z-ketotetrahydro-1,3-oxazine by effecting reaction bet-ween equimolecular' proportions (or with the one reactantfrom,.forexample, 0.01 to 10 mole percent in excess of the other) of 3-aminopropanol and a dialkyl carbonate, e. g.', diethyl carbonate, dipropyl carbonate, etc., to obtainrthe corresponding N-(3-hydroxyp1'opyD-O- alkyl carbamate, distilling off the alcohol by-product of the initial reaction, and continuing the distillation under heat (usually also under vacuum) to remove the remaining combined alcohol, whereby the N-(3-hydroxypropyl)- Oka-lkyl carbamate is cyclized and 2-ketotetrahydro1,3-

oxa'zine is formed, after which the said 1,3-oxazine is isolated, e. g., by distillation, from the reaction mass. The temperature required for removing the remaining combined alcohol and forming the 1,3-oxazine varies depending, for example, upon the particular alcohol to be removed and the vacuum (if any) employed, e. g., from '40" C. to 200 C.

The conversion of the N-(3-hydroxypropyl)-O-alky1 carbamate to the cyclic carbamate, whereby combined alcohol is evolved, is preferably carried out with the aid of an alcoholysis catalyst. Examples of such catalysts which may be used are alkali metals, alkaline-earth metals and certain heavy metals (e. g., lead, zinc, manganese, etc) or oxides, carbonates or salts thereof. Any suitable amount of an alcoholysis catalyst can be employed, as desired or as conditions may require, c. g., from 0.000l%' to 1 or 2% by weight of the intermediate, N-( 3-hydroxypropyl)-O-alkyl carbamate.

During thepreparation of the cyclic carbamate and its isolation by distillation, some polymer of the carbamate also is formed in varying amounts and remains in the residue.

The polymer of the carbamate also can be produced by isomerizat'ion of theisolated monomer, e. g., by heating the said monomer at temperatures ranging from about 40 to 200 C. The isomerization can be accelerated by the use of a suitable catalyst or catalysts, for instance, traces of a monohydric alcohol (e. g., methyl, ethyl, propyl, etc., alcohols), or of an alkali-metal carbonate, e. g., potassium carbonate, etc., or of a Friedel-Crafts catalyst, e. g., zinc chloride, aluminum chloride, sulfuric acid, hydrogen fluoride, boron trifluoride, BFs-ethyl ether complex, etc. Traces of water also may sometimes be used advantageously as a polymerization catalyst. With certain catalysts, for example Friedel-Crafts catalysts, the isomerization of the monomer to a polymer may be effected at temperatures substantially below 40 C., for instance at from 80 C. to 20 or 30 C., in which case the reaction is usually effected in a liquid medium which is inert during the reaction and in which the monomer can be dissolved or readily dispersed.

In order that those skilled in the art may better understand how the present invention can be carried into effect, the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight.

Example 1 To a reaction vessel is added 118 parts of diethyl carbonate at 25 C., after which 75 parts of 3aminopropanel is added with stirring. This is in the ratio of 1 mole of diethyl carbonate to 1 mole of 3-aminopropanol. Initially a two-phase system forms in the reaction vessel; however, when the reaction mass is stirred for about l6 hours at room temperature (25 -30 C.), it becomes clear and homogeneous.

The reaction vessel is now fitted with a column and a distillation head. An alcoholysis catalyst, e. g., a few shavings of metallic sodium (about 0.5 part), are added to the reaction mass comprising the intermediate reaction product, HO(CH2)3NHCOOC2H5, and the ethanol byproduct of the initial reaction is removed by distillation. Some of the combined ethanol is removed at the same time. In this distillation 72 parts of volatile matter comprising mostly ethanol and boiling at 78-80 C. is recovered. After changing the apparatus for vacuum distillation, an additional 18 parts of volatile matter (also comprising chiefly ethanol) is removed under vacuum. About 10% of this material is apparently not ethanol. The total conversion is then calculated as follows:

Vacuum distillation is continued with the pressure lowered to 1.5 to 2 mm. mercury while gradually raising the temperature. At a vapor temperature of l50-155 C. a yellow, viscous oil comprising 2-ketotetrahydro-1,3- oxazine is distilled off. This oil is collected in areceiver surrounded by Dry Ice and wherein it solidifies. After collecting 35 parts of this material, the vapor.temperature in the distilling head drops sharply and no more distillate is recovered.

The residue in the reaction vessel is a dark brown resin (polymer of Z-ketotetrahydro-l,3-oxazine) which, even when hot, can be poured only with difiiculty. It has an average molecular weight substantially above 10,000 as calculated from viscosity measurements of a dilute solution using the Staudinger equation. It is a fiber-forming material. Fibers or filaments can be formed from this polymer by conventional melt-extrusion technique or by other means. The extruded filaments can be drawn either hot or cold. The drawn or stretched fibers or filaments show, by characteristic X-ray patterns, orientation along the fiber axis.

The monomeric reaction product comprising Z-ketotetrahydro-l,3-oxazine is a liquid at room temperature (2530 C). It is readily soluble in water, methanol and benzene but is insoluble in hexane. Attempts to recrystallize it from solvent and non-solvent mixture e. g., mixtures of hexane and benzene, and of hexane and methanol, result in oiling out of the liquid product. From the setting-point curve a melting-point value of 212 C.-21.4 C. is obtained.

The above reaction may be illustrated by the following equation:

H2N(CH OH (CzHsOMCQ hydro-1,3-oxazine In the above equation n represents the number of the recurring units in the polymer molecule, e. g., from 2 to 1000 or more. The dimers, trimers, tetramers, pentamers, hexamers and other lower-molecular-weight prodnets, and mixtures thereof, can be used in various industrial applications, for instance as plasticizers for resinous aldehyde-reaction products of urea, aminotriazines (e. g., melamine) or other amidogen compounds, as well as for plasticizing other compatible resinous materials which normally are deficient in plasticity or flow characteristics. As has been indicated hereinbefore, the higher-molecular-weight, normally solid polymers are useful in making fibers (including both monoand multifilamerits).

Example 2 To 12 parts of sulfuric acid is added 10 parts of tetramethylene hydroximic acid. This mixture is heated cautiously until bubbles first appear. The heating is discontinued and the violent reaction which ensues permitted to subside. This acid solution is cooled to 0 C. and carefully made alkaline with 24% potassium hydroxide solution, taking care to keep the temperature below 10 C. with adequate cooling at all times. The potassium sulfate which separates is washed twice with 5 parts of chloroform. The neutral filtrate is extracted five times with 10 parts of chloroform. The combined chloroform extracts are washed with 5 parts water to eliminate traces of alkali. Removal of the chloroform solvent yields and desired 2-ketohexahydro-1,3-oxazepine.

Similar technique can be used in making 2-ketotetrahydro-1,3-oxazine from trimethylene hydroximic acid.

Example 3 To parts of the isolated Z-ketotetrahydro-1,3-oxazine of Example 1 is added 1 part of potassium carbonate. The resulting mixture is heated for 2 hours While passing a slow stream of pre-purified nitrogen gas over the mass. During this heating period the liquid monomer thickens considerably. Heating is continued for an additional 8 hours under the same conditions, yielding a hard polymer of the starting 1,3-oxazine.

It was quite surprising and unexpected that the 6- and 7-membered cyclic carbamates could be isomerized to linear polymers, since the corresponding S-membered cyclic carbamates do not undergo this isomerization.

In my copending application Serial No. 549,889, filed November 29, 1955, as a division of this application, claims are made to a method of preparing a new polymeric materialwhich comprises isomerizing to a linear polymer a cyclic carbamate represented by Formula I,

5 I claim: 1. The method of preparing a cyclic carbamate represented by the general formula where n represents a whole number selected from the class consisting of 3 and 4, said method comprising effecting a Beckmann rearrangement, using sulfuric acid as a catalyst for the reaction, of the corresponding hydroximic acid represented by the general formula where n has the same meaning as given above with reference to the first-named formula, and isolatinga cyclic carbamate represented by said first-named formula from the resulting reaction mass.

2. The method of preparing a cyclic carbamate represented by the general formula 7 Ta which comprises efiecting a Beckmann rearrangement, using sulfuricacid as a catalyst for the reaction, of the corresponding hydroximic acid represented by the general formula HO-N and isolating Z-ketotetrahydro-LS-oxazine from the resulting reaction mass.

3. The method of preparing a cyclic carbamate represented by the general formula which comprises eflzecting a Beckmann rearrangement,

using sulfuric acid as a catalyst for the-reaction, of the corresponding hydroximic acid represented by the general formula HO-N . 'OI/- (CH2)4. and isolating 2-ketohexahydro-1,3-oxazepine from the resulting reaction mass.

References Cited in the file of this patent UNITED STATES PATENTS Martin Nov. 28, 1939 OTHER REFERENCES Sidgwick: The Org. Chem. of Nitrogen (1937), pp.

Morton: The Chem. of Heterocyclic Cpds." (1946),

pp. 23 1, 274, 342, 372and 499. 

1. THE METHOD OF PREPARING A CYCLIC CARBAMATE REPRESENTED BY THE GENERAL FORMULA 